An antigen restricted to gastrointestinal tissues and to some mucinous ovarian tumors has recently been identified. (Goldenberg et al, Proc. Am. Assoc. Cancer Res., 17, 155 (1976); Pant et al, Immunol. Commun., 6, 441 (1977); and Pant et al, Cancer, 42, 1626 (1978)). This antigen is called colon-specific antigen-p(CSAp), and is characterized by its heat-lability, phenol-sensitivity and its sensitivity to thiolic and chaotropic reagents. CSAp is immunologically distinct from other gastrointestinal antigens, including the family of phenol-soluble, heat-stable colonic organ-specific antigens called colon-specific antigens (CSA) which are found in both normal, diseased and neoplastic gastrointestinal tissues, particularly the colon and rectum. In addition, CSAp is immunologically distinct from carcinoembroyonic antigen (CEA), colonic mucoprotein antigen (CMA), zinc glycinate marker (ZGM), beta-oncofetal antigen (BOFA) and blood group antigens.
The earlier attempts to characterize CSAp suggested that the antigen has a molecular size in the range 70,000-120,000 (molecular size herein is always understood to be expressed in atomic units). However, it is now clear that native CSAp was lost during processing in these earlier experiments, and that the lower molecular weight species having CSAp antigenic activity were artifacts resulting from fragmentation of the native molecule during tissue homogenization. All previous CSAp antigenic preparations were heterogeneous mixtures of antigens having a wide range of molecular weights. These materials were difficult to purify and characterize.
The level of CSAp has been found to increase in neoplasia and in certain other diseased tissues of the colon, including morphologically normal colonic mucosa adjacent to adenocarcinoma, in Pant et al, Cancer, 42, 1626 (1978). Recent results indicate that CSAp is useful in the immunodiagnosis and radioimmunodetection of colorectal cancer.
A need therefore continues to exist for a method of producing a purified, immunologically active antigen having CSAp antigenic activity, and for an improved method of producing monospecific antibodies to CSAp.